Variable speed hydrostatic drive

ABSTRACT

A hydrostatic drive is operated to provide the required demand horsepower of a particular load and speed condition while maximizing the loading of the input prime mover. The prime mover speed control and the variable displacement control lever of a hydrostatic pump are interconnected by a sliding cam such that the available power output of the prime mover is coupled to the driven load with sufficient power at the minimum prime mover speed where this power is developed. This extends the useful life and reduces the fuel consumption of the prime mover. The overall efficiency of the drive system is improved.

United States Patent [191 Tone [111 3,826,097 1 July 30, 1974 VARIABLESPEED HYDROSTATIC DRIVE [76] Inventor: John W. Tone, 2601 Foulk,

Wilmington, Del. 19810 Primary ExaminerEdgar W. Geoghegan AssistantExaminer H. Burks Attorney, Agent, or Firm-Mortensen & Weigel 57]ABSTRACT A hydrostatic drive is operated to provide the required demandhorsepower of a particular load and speed condition while maximizing theloading of the input prime mover. The prime mover speed control and thevariable displacement control lever of a hydrostatic pump areinterconnected by a sliding cam such that the available power output ofthe prime mover is coupled to the driven load with sufficient power atthe minimum prime mover speed where this power is developed. Thisextends the useful life and reduces the fuel consumption of the primemover. The overall efficiency of the drive system is improved.

7 Claims, 6 Drawing Figures PATENIEU- Flow flew aszky' FM VARIABLE SPEEDHYDROSTATIC DRIVE BACKGROUND OF THE INVENTION This invention relates toa variable speed hydrostatic drive that increases the loading on aninput prime mover while meeting the required demand horsepower of a loadand yet is relatively simple in construction.

There are many drive systems known which have a conventional directdrive, mechanical or otherwise, operating with a fixed reduction ratio.The term reduction ratio means the power output shaft driving the loadoperates at a lower angular velocity than does the prime mover and therelationship between these velocities is fixed.

In a typical case, the load to be driven has a demand horsepowerrequirement which varies as a function of the speed with which the loadis to be driven. This load may be a locomotive, a marine or othervehicle, or a machine drive. At the same time, the prime mover for thesystem develops a certain horsepower which varies as a function of theangular velocity of the prime mover output shaft. Unfortunately, sincethese two relationships are not represented by the same function, oftenthe prime mover must overspeed and consume excess fuel to satisfy therequired angular velocity requirements of the load. This results inexcessive fuel consumption due to the frictional and compression pumpinglosses in the engine and increased wear and fatigue of 'parts operatingat higher speeds.

More recently various automatic systems have been developed foroptimizing the efficiency of the engine and transmission. Unfortunately,many of these systems are relatively complicated, costly, and tend tobecome unreliable due to their very complexity.

It is, therefore, an object of this invention to obviate the manydisadvantages of the prior art drive systems.

BRIEF DESCRIPTION OF THE INVENTION In a preferred embodiment of theinvention, a hydrostatic drive system for a load having a known powerdemand versus speed characteristic includes a first prime mover having afirst adjustable control means for varying the speed of the prime mover,a first reversible and adjustable fluid pump adapted to be driven by theprime mover and having a second adjustable control means for varying thefluid displacement of the pump, a first hydraulic motor hydraulicallyconnected to the pump and adapted to drive the load at speeds related tothe speed of the motor. The system also includes a 'first master controlmeans connected to the first and second control means for relativelyadjusting the speed of the prime mover and the displacement of the pump.A manual means is included for setting the first master control meansfor a desired load speed. The first master control means operates toadjust the speed of the prime mover to the minimum required to meet thepower demand of the load at a desired speed.

The first master control means in a preferred embodiment includes firstand second cam means having corresponding first and second cam surfacesand first and second cam followers respectively coupled to the first andsecond control means. The first and second cam followers are associatedrespectively with the first and second cam surfaces, thereby to permitthe simultaneous adjustment of the first and second control means inaccordance with the setting of the manual means for matching the primemover horsepower to the demand horsepower of the load for all desiredspeeds in both forward and reverse directions.

In other embodiments of the invention, two hydraulic motors are drivenby the same pump. A slide valve arrangement controls the fluid flow tothe two motors such that by placing the motors side by side in a boatfor example, and varying the fluid directed to each motor, the boat maybe steered without the use of a rudder. This appreciably reduces thedrag losses of the rudder and steering assemblages. Still otherembodiments include the utilization of a single joy-stick to controlboth boat speed and direction without need of a rudder while stillmatching demand horsepower of the load to prime mover output at minimumprime mover speed.

BRIEF DESGRIPTION OF THE DRAWINGS The novel features that are consideredcharacteristic of this invention are set forth with particularity in theappended claims. The invention, itself, however, both as to itsorganization and method of operation, as well as additional objects andadvantages thereof, will be best understood from the followingdescription when read in connection with the accompanying drawings, inwhich:

FIG. 1 is a combination plot of the ship demand horsepower, engine shafthorsepower, and propeller speed against ship speed and engine speeddepicting the various relationships such as demand horsepower versusship speed, engine horsepower versus engine rpm. and propeller speedversus ship speed for a particular internal combustion engine and aparticular ship;

FIG. 2 is a block diagram depicting a marine hydrostatic-drive systemconstructed in accordance with this invention utilizing a controlmechanism for matching the engine horsepower to the demand horsepower ofthe ship throughout the ships speed range;

FIG. 3 is an elevation view of a slide cam arrangement which may be usedto implement the control mechanism illustrated in FIG. 2;

FIG. 4 is a block diagram of a ship hydrostatic drive system in whichtwo hydraulic motors are employed to effect ship steering as well aspropulsion, with a single prime mover and a single variable displacementpump;

FIG. 5 is a block diagram partly in pictorial representation of avariable speed hydrostatic drive system for a ship utilizing two primemovers and twin propellers for effecting ship steering in which a singlecontrol lever is utilized to control both ship speed and direction;

FIG. 6 is an elevation view of a slide cam arrangement adapted tocontrol engine speed, pump displacement and motor displacementsimultaneously in order to match the ship demand horsepower to theengine horsepower while maintaining minimum engine speed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS There is seen in FIG.I the various curves depicting te relationship between a typical primemover or internal combustion engine horsepower plotted in curve 14, as afunction of engine angular velocity and the ship demand horsepower curveplotted as a function of ship speed. In addition, the ship performancerelation, i.e., propeller speed versus ship speed relationship isplotted as curve 12. From these curves l0, I2, 14 it may be seen thatwith a conventional direct drive or a drive having a fixed reductionratio, the engine must overspeed and consume excessive fuel in order tosatisfy the required propeller angular or rotational velocity throughoutthe ships performance range. It may be noted from these curves thatpropeller speed increases almost linearly in proportion to the shipspeed except for small changes in efficiency of the propeller throughoutits speed range. It may be seen also that in the low range of a shipsspeed, such as 5 miles per hour (m.p.h.), the propeller angular velocityor speed needed to drive the ship is 240 revolutions per minute at theminimum engine speed of 600 rpm, which is the engine idle speed.Further, at the maximum speed that the propeller must turn, which inthis instance is 1,000 rpm, the engine speed is 2,500 rpm, thereforindicating a reduction ratio of 240/600 l/2.5 at low speeds and1,000/2,500 l/2.5 at maximum speed. With these fixed reduction ratios of1 to 2.5 which is typical of a conventional drive, it is seen that forevery revolution of the propeller, the engine turns 2 /2 revolutions.

To illustrate the losses that occur in a direct drive system of thistype with no variation of the ratio throughout the speed range, twotypical speeds may be examined to determine the fuel consumption. Thus,if a ship speed of 15 m.p.h. is selected, according to FIG. 1 apropeller speed of 750 rpm would be required. Similarly, with thereduction ratio of 1/2.5 the engine must run at 1,875 rpm. At this speedthe engine can develop a horsepower of 55. However the ship onlyrequires 37.5 horsepower to reach this speed as seen from curve 10.

If on the other hand an appropriate variable speed transmission wereused, at 15 m.p.h. the demand horsepower of 37.5 horsepower can begenerated by the engine at 1,250 rpm as may be seen from the enginehorsepower curve 14. Since the required propeller speed is only 750 rpmas determined previously, it would be desirable to use a reduction ratioof 750/1,875 l/l.66.

It is a well established fact that the specific fuel consumption, i.e.,gallons or pounds per horsepower per hour is substantially reduced whenan internal combustion engine is run in a loaded condition, i.e.,absorbs its rated horsepower at a given rpm as compared to the lowpercentage loading as shown in FIG. 1, i.e., 33 percent at 5 m.p.h. and70 percent at 15 m.p.h. The savings in fuel consumed vary with thedegree of loading, but are in the order of l 1 percent for a four cycleengine and percent for a two cycle engine in the example described.

A ship typically cruises at 80 percent of its maximum speed to extend,the engine life. In the example illustrated in FIG. 1 a cruising speedof 0.8 X 20 m.p.h. 16 m.p.h., with a conventional fixed reduction geardrive, the engine speed equals 2,000 rpm. With the variable drive theengine speed is only 1,450 rpm, which is very close to the maximumtorque point of the engine described. At the maximum torque point, thebest efficiency possible is obtained from the engine (lowest specificfuel consumption).

The life of the engine is greatly increased at these lower rpms sincethere is a modest increase in the b.m.e.p. (brake mean effectivepressure) but the inertia forces, which vary as the square of the speed,are almost reduced to 50 percent and the pumping (compression andexhaust) work and friction losses are reduced. The life of the engine isgreatly increased.

It is thus apparent that for any ship or other load, for that matter,that has a known engine horsepower versus rpm relationship and a knownpropeller pitch (advance per revolution), an appropriate reduction ratioversus ship speed relation can be plotted. If one also knows therelationship of the position of the control lever, which controls thethrottle of an otto cycle motor or the injection pump of a diesel motor,for example, to engine horsepower, the engine speed and pumpdisplacement may be varied according to the desired speed of the ship toachieve maximum efficiency between the engine and the ship propellerthroughout the speed range of the ship.

One such system for accomplishing this is illustrated in FIGS. 2 and 3.Thus, in FIG. 2 there is seen a prime mover 20 which is connected todrive the shaft of a reversible and adjustable hydraulic pump 22. Inturn the pump 22 is connected through fluid conduits 24 and 26 to areversible fixed displacement hydraulic motor 28. The hydraulic fluidfrom the pump 22 circulates through one or other of the lines 24-26 todrive the motor 28 in either a clockwise or counterclockwise directionas is well known in the art. In turn the output of the motor 28 isconnected through a shaft 30 to drive a propeller 32 which, when mountedin a suitable boat or ship hull, may provide the necessary propulsionpower for the ship.

The prime mover 20 may be a conventional internal combustion motor suchas a diesel engine or conventional gasoline driven engine. In any event,the prime mover 20 has an adjustable control means 34 which controls theamount of the fuel supplied to the engine. This control means 34 in thecase of a diesel engine may be the control rod monitoring the injectionpump. In the case of the gasoline engine, it may be the throttle whichcontrols the flow of gas through the carburetion system.

In like manner, the pump 22 may be any conventional variabledisplacement hydraulic pump as a piston pump of well known type. In anyevent, the pump 22 has an adjustable control arm 36 for varying thedisplacement of the pump and hence the volume of fluid flow through thepump and also the direction of fluid flow through the pump. Both theprime mover control means 34 and the pump control arm 36 are connectedto a master control mechanism 38 which operates under the impetus of ahand or manual control depicted by the lever 40 pivoted about the fixedpoint 42 and operating through the linkage 44 to operate the mastercontrol means 38. The master control means 38 in turn varies therespective control links 34 and 36 as a function of the necessary shipdemand and prime mover horsepower versus rpm and propellerrelationships, respectively, in accordance with this invention, tooperate the prime mover at the minimum speed that will develop thehorsepower required to move the ship at this desired speed. Statedanother way, the master control means 38 matches the engine power to thedemand horsepower of the ship throughout the ship speed range.

The details of a preferred control mechanism 38 are illustrated in FIG.3. This control mechanism functions to allow the pump control arm 36 topass through neutral (zero output) coincident with an engine throttleidle position. The function is required for both starting the enginewithout load and also to permit the engine to pass through this phasewhen reversing. This is necessary to prevent stalling the engine. Themechanism illustrated in FIG. 3 is a slide cam mechanism in which themanual control arm 40 is pivoted at a fixed pivot point 42 and operatesthrough a pivoted linkage 44 connected to the mid-point 46 of the manualcontrol 40 to a slide cam 48 in the form of a plate having a curved slotor cam 50 formed therein. The slot 50 provides a cam surface againstwhich a cam follower 52 may move as the cam 48 is slid back and forth(left to right in the drawing) within a pair of guide blocks 54. The camsurface 50 is noted as being somewhat Z-shaped with the cam followers 52being depicted in neutral position. The cam follower is connected to thelever 36 which is connected to the control arm 36 of the pump.

Attached to a projecting slotted tab 58 on the end of the slide cam 48there is secured, as by adjusting screws 60, a throttle control camplate 62. The upper surface of the throttle control cam plate 62includes the cam 64 which, operating through a cam follower 66, operatesto control the prime mover or engine speed. The cam follower 66 isattached to the end of the throttle control linkage 34 which is urgeddownwardly against the cam surface 64 by means of a suitable spring 68.A manual pull-to-stop control 70 is also illustrated. This pull-to-stopcontrol has a handle 72 which is secured through a shaft to a pivotedslot assembly 74 at the lower end thereof (in the drawing). The slot 74engages a pin 76 attached to the side of the engine throttle control arm34 such that by lifting the handle 72 the control arm 34 is raised up tocut the engine below its idle speed. The slot 74 is of sufficient lengthto permit the cam follower 66 to follow the cam surface 64 duringoperation of the slide cam.

The throttle control arm 34, in the position illustrated, is in theengine idle position. As the follower 66 drops (in the drawing) orrotates in a counterclockwise direction, the engine speed is increasedto a maximum as depicted by the phantom position of the follower 80. Inlike manner, the position illustrated for the pump control arm 36 is inneutral position, i.e., no fluid flow. As the follower 52 drops (in thedrawing) such as to the lowermost position illustrated by the phantomlines 92, the fluid flow from the pump increases and is in such adirection as to drive the motor in a forward direction at full pumpdisplacement and decreased reduction ratio of the hydraulictransmission. Conversely, as the follower moves upwardly, to theposition depicted in phantom at 94, the pump is operated in a fullreversed flow sense and the reduction ratio of the hydraulictransmission is reduced.

Thus, in an assumed operation, the operator moves the manual control arm40 in a forward direction from the neutral position N, thereby movingthe slide cam plate to the left in the drawing. The pump control arm 36increases the fluid flow into the fluid motor in a forward sense fromzero. As the manual control 40 continues to move to the left in thedrawing so as to increase forward speed, the speed of fluid flow isincreased until a maximum is achieved after which, due to the Z-shape ofthe cam surface 50, the flow is again decreased thereby increasing thereduction ratio of the transmission in order to match ship power to thepropeller rpm.

This same movement of the manual control lever 40 from the neutral oridle position also causes the throttle cam 66 to move downwardly in thedrawing allowing the engine speed to be increased, slowly at first andthen at an increasing rate. The same control function prevailsregardless of whether the manual lever is moved for forward or reversespeed. with this arrangement, it may be seen that the ship demandhorsepower is matched by the engine horsepower and yet the engine isoperated at minimum rpm in all cases.

Referring to FIG. 1, it is seen that at low ship speeds the ship demandhorsepower increases relatively slowly with increased ship speed.Conversely, the engine developed horsepower increases rather quicklywith increased ship speed. This accounts for the different slopes of thecam surfaces 64 and 50 for the engine and motor respectively. Thesevarying functions result in a varying reduction ratio. A similaranalysis may be made for the reverse direction, however, this is notbelieved necessary to the understanding of this invention. Virtually anycontrol function can be achieved by proper shaping of the cam surfaces.

There is seen still another embodiment of this invention in the drawingof FIG. 4. In this illustration the system incorporates the sameelements as tnose shown in FIG. 2 up through the pump 22. From thispoint on, the fluid lines 24 and 26 are connected to a sliding spoolvalve 100. Alternatively, a cam actuated poppit valve may be used.Whichever valve is used, it controls the equal or differential flow totwo separate fixed displacement hydraulic motors 28 and 28. Fluid lines102-104 connect the fluid flow from the poppit valve to the motor 28wherein lines 102 and 104 connect the poppit valve to the second motor28'. The motors in turn are connected to propellers 32 and 32'respectively. By adjustably controlling the fluid flow to theserespective motors, steering of the ship may be accomplished by varyingthe load, i.e., the speed of the propellers 32 and 32'.

The sliding spool valve 100, which functions to divide the flow from thefluid lines 24 and 26 to the respective motors 28 and 28' is controlledby an actuating arm 106 which is operated by the linkage 108 which inturn is connected to be controlled by a cable 110 connected to rack andpinion gears 112 and 114 respectively. The pinion gear 114 is rotatedby, for example, a ships steering wheel 116. Thus rotation of the wheel116 imparts lineal motion to the cable 110 which operates the linkage108. This linkage is illustrated as a second class lever to reduce themotion imparted by the cable and thereby operate the actuating member106 of the spool valve 100 to vary the fluid flow to the respectivemotors 28 and 28'. This increases or decreases the speed of therespective propellers 32 and 32' and effects steering of the ship asnoted without varying the load, i.e., the speed of the prime mover 20.

Another alternative embodiment of this invention is illustrated withreference to the block diagram of FIG. Sin which there is illustrated atwin prime mover installation which includes two parallel engines 20 and20', pumps 22 and 22, fluid lines 24-26 and 24'26', fixed displacementmotors 28 and 28 and propellers 32 and 32'. The motors and propellersare preferably positioned on a ship on widely separated propellercenters to enhance the ability to steer the ship without the aid of arudder. As noted herein before this eliminates the rudder drag losses.

Master control means 38 and 38' are provided for the respective drivesystems. Each control means 38 and 38' is controlled by respectivepush-pull cables 120 and 12.0 which in turn are connected betweenrespective master controls 38 and 38 and the output control arms 122 and122 of a differential control lever. A suitable control for this purposeis one manufactured by Morse Controls and is designated as Type 34OX2.This control includes a central control lever 124 which is connected toa ball pivot 126. An output control arm 128 extends diametricallythrough the ball pivot 126 to operate the control arms 122 and 122.

Thus forward and reverse movement, as denoted by the arrows 130, of thecontrol stick 124 causes the cables 120 and 120' to move back and forthequally. In like manner, sideways movement of the control stick designedby the arrows 132 cause the two cables 120 and 120 to move back andforth differentially with respect to each other to operate the mastercontrol means 38 and 38'. A combination of sideways and forward andreverse movement of the control stick produces a combination movement.

The remainder of the operation of the system is substantially the sameas that previously described except for the fact that twin drivesystems, are employed. Thus, by varying the reduction ratio of the twodrive systems, the ship may be maneuvered quite well at all speeds,turned, backed up, etc. Further, the demand horsepower of the load ismet with minimal engine speed with the attendant advantages set forthhereinbefore.

Still another alternative embodiment of this invention is illustrated inFIG. 6 which allows a greater speed change range. In FIG. 6 there isshown an alternative master control means that may be employed in theevent, for example, the motors 28 and 28' illustrated in FIG. or any ofthe other figures, for that matter, are selected to be variabledisplacement motors so that they may be adjusted to operate at differentspeeds for the same fluid flow rate. In this event, the master control38 may constitute a slide cam arrangement as illustrated in FIG. 6. Inthis arrangement, the control lever is linked as by 44 to the slide camplate 150 which is adapted to slide within suitable bearings depicted at152. The cam plate 150 has slots which define a pair of cam surfaces 154and 170 in which cam followers 156 and 172, respectively, arepositioned. The first cam follower 156 is connected by the linkage 158to operate the hydraulic pump control lever 36 (FIG. 1). The second slotwhich forms the second cam surface 170, positions the motor control camfollower 172. This cam follower 172 is connected to the linkage 174which is coupled to the adjustable displacement control lever of thehydraulic motor (not shown). In similar manner the upper portion (in thedrawing) of the slide cam 150 is shaped to provide a cam surface 160 forcontrol of the adjusting control lever of the prime mover. In thisinstance the cam follower 162 is coupled through a linkage 164 tooperatethe control lever 34 (FIG. 1) of the prime mover.

The particular configuration of the cam surfaces 154, 170 and willdepend of course upon the characteristics of the respective pumps, load,motor and the like. Certain of these characteristics are readilyobservable from an inspection of the drawing. For example, both themotor and pump must pass through the neutral position before going fromforward to reverse. At this point, of course, the prime mover must beoperating at idle speed. This is the condition illustrated in FIG. 6. Ineach instance, the cam configuration is such as to match the requiredload at minimum speed of the prime mover.

There has thus been described a relatively simple system by which thereduction ratio in the transmission comprising a hydraulic pump andmotor is varied continuously throughout the speed range of the vehicleor other object being driven in order to provide the demand horsepowerfor the load at the minimum engine speed. This result is obtained by theutilization of what preferably may be a slide cam arrangement with norequirement for relatively expensive, complex sensors and other servocontrols. Alternatively, of course, a more sophisticated servo systemmay be substituted for the simple slide cams illustrated in order toobtain the desired control relationships described herein. With thisinvention considerably savings in fuel are achieved. Also, in theapplication to a ship significant increase in maneuverability is had.Wear and tear on the prime mover is reduced since it is always operatedat minimum speed.

It is obvious that many embodimemts may be made of this inventiveconcept, and that many modifications may be made in the embodimentshereinbefore described. Therefore, it is to be understood that alldescriptive matter herein is to be interpreted as illustrative,exemplary and not in a limited sense.

What is claimed is:

l. A hydrostatic drive system for a load having a known power demandversus speed characteristic comprising:

a first prime mover having a first adjustable control means for varyingthe speed of said prime mover,

a first reversible and adjustable fluid pump adapted to be driven bysaid prime mover and having a second adjustable control means forvarying the fluid displacement of said pump,

a first hydraulic motor hydraulically connected to said pump and adaptedto drive said load at speeds related to the speed of said motor,

first master control means connected to said first and second controlmeans for adjusting in a predetermined fixed relationship the speed ofsaid prime mover and the displacement of said pump according to theknown power demand of said load at any desired speed, and

a manual means for setting said first master control means for a desiredload speed, said first master control means operating to adjust thespeed of said first prime mover to the minimum required to meet thepower demand of said load at said desired speed.

2. A system according to claim 1 wherein said first master control meansincludes:

first and second cam means having corresponding first and second camsurfaces which are related to the horsepower characteristic of saidload,

first and second cam followers respectively coupled to said first andsecond control means,

said first and second cam followers being associated respectively withsaid first and second cam surfaces, thereby to permit the simultaneousadjustment of said first and second control means in accordance with thesetting of said manual means for matching the prime mover horsepower tothe demand horsepower of said load for all desired speeds.

3. A system according to claim 2 wherein said prime mover is acombustion engine and said first control means controls the fuelsupplied to said engine.

4. A system according to claim 2 wherein said load is a ship and saidsecond cam means is shaped to cause said second cam follower to increasethe displacement of said pump to a maximum and thereafter reduce saidpump displacement as a function of the increasing speed and powersetting of said manual means for both forward and reverse fluid flow.

5. A system according to claim 4 wherein said second cam surfaceincludes a position between forward and reverse settings of said camfollower corresponding to no fluid flow in saidpump.

6. A system according to claim 1 wherein said first hydraulic motor isadjustable and reversible and said system includes third adjustablecontrol means for varying the fluid flow in said first motor, saidmaster control means being also connected to said third control meansfor adjusting the fluid flow in said first motor according to thehorsepower characteristic of said load, thereby to more closely optimizethe operating characteristic of said prime mover, said pump and saidmotor.

7. A system according to claim 6 wherein said first master control meansincludes:

first, second and third cam means having corresponding first, second andthird cam surfaces,

first, second and third cam followers respectively coupled to saidfirst, second and third control means,

said first, second and third cam followers being associated respectivelywith said first, second and third cam surfaces, thereby to permit thesimultaneous adjustment of said first, second and third control means inaccordance with the setting of said manual means for matching the primemover horsepower to the demand horsepower of said load for all desiredspeeds.

1. A hydrostatic drive system for a load having a known power demandversus speed characteristic comprising: a first prime mover having afirst adjustable control means for varying the speed of said primemover, a first reversible and adjustable fluid pump adapted to be drivenby said prime mover and having a second adjustable control means forvarying the fluid displacement of said pump, a first hydraulic motorhydraulically connected to said pump and adapted to drive said load atspeeds related to the speed of said motor, first master control meansconnected to said first and second control means for adjusting in apredetermined fixed relationship the speed of said prime mover and thedisplacement of said pump according to the known power demand of saidloAd at any desired speed, and a manual means for setting said firstmaster control means for a desired load speed, said first master controlmeans operating to adjust the speed of said first prime mover to theminimum required to meet the power demand of said load at said desiredspeed.
 2. A system according to claim 1 wherein said first mastercontrol means includes: first and second cam means having correspondingfirst and second cam surfaces which are related to the horsepowercharacteristic of said load, first and second cam followers respectivelycoupled to said first and second control means, said first and secondcam followers being associated respectively with said first and secondcam surfaces, thereby to permit the simultaneous adjustment of saidfirst and second control means in accordance with the setting of saidmanual means for matching the prime mover horsepower to the demandhorsepower of said load for all desired speeds.
 3. A system according toclaim 2 wherein said prime mover is a combustion engine and said firstcontrol means controls the fuel supplied to said engine.
 4. A systemaccording to claim 2 wherein said load is a ship and said second cammeans is shaped to cause said second cam follower to increase thedisplacement of said pump to a maximum and thereafter reduce said pumpdisplacement as a function of the increasing speed and power setting ofsaid manual means for both forward and reverse fluid flow.
 5. A systemaccording to claim 4 wherein said second cam surface includes a positionbetween forward and reverse settings of said cam follower correspondingto no fluid flow in said pump.
 6. A system according to claim 1 whereinsaid first hydraulic motor is adjustable and reversible and said systemincludes third adjustable control means for varying the fluid flow insaid first motor, said master control means being also connected to saidthird control means for adjusting the fluid flow in said first motoraccording to the horsepower characteristic of said load, thereby to moreclosely optimize the operating characteristic of said prime mover, saidpump and said motor.
 7. A system according to claim 6 wherein said firstmaster control means includes: first, second and third cam means havingcorresponding first, second and third cam surfaces, first, second andthird cam followers respectively coupled to said first, second and thirdcontrol means, said first, second and third cam followers beingassociated respectively with said first, second and third cam surfaces,thereby to permit the simultaneous adjustment of said first, second andthird control means in accordance with the setting of said manual meansfor matching the prime mover horsepower to the demand horsepower of saidload for all desired speeds.